INFLUENCE OF DESIGN OF NUCLEAR WASTE DISPOSAL CONTAINERS ON CORROSION OF IRON-BASE MATERIALS IN SALT BRINES

摘要

In the present work, the influence of the double-walled design of a spent fuel disposal container on the long-term corrosion behavior of preselected iron-base container materials was investigated in two disposal-relevant salt brines at 150 deg C. For the investigations model container were used. These consisted of a container made of the low-alloyed steel 15MnNi6.3 (disposal container for mechanical and corrosion protection) which was surrounded by a cast iron container (shielding against gamma radiation). The results indicate that the general corrosion rates of 15MnNi6.3 steel and cast iron determined on the double-walled model containers are significantly lower than previous values obtained on small metal coupons of these materials simulating a single-walled container design. The extremely low general corrosion rates of the inner 15MnNi6.3 steel container (about 1 gm/y to 1.5 gm/y) are attributed to the fact that the annular gap between the both containers is filled with solid iron-corrosion products and precipitated salts which restrain the transport of additional brine to the annular gap. The smaller corrosion rate of the outer cast iron model container compared to the small cast-iron coupons can be explained by the reduced initial brine availability in the model container experiments.